Push-to-talk (PTT) is a two-way communication service that works like a walkie-talkie. A normal cell phone call is full-duplex, meaning both parties can hear each other at the same time. PTT is half-duplex, meaning communication can only travel in one direction at any given moment. A token-based model of operation, in which a person must be first granted access to the floor by a floor control mechanism before he may speak to other session participants, typically governs most PTT sessions. For instance, a PTT-enabled handset typically requires that a caller press and hold a button while talking, and then release the button when they are done. Any listener may then press their button in a similar manner to request access to the floor in order to respond.